In the manufacture of general purpose telephone sets, a molded plastic housing of the set is assembled with a base member of the set by threaded fasteners, such as machine screws. For this purpose, the housing is formed with a series of upstanding tubular plastic sleeves or bosses, each having an axial bore into which an insert member, such as an internally threaded tubular receptacle for receiving the machine screw, is to be force fit during manufacture of the housing. In the plastics molding operation, the boss is formed with a weld line extending radially across an annular wall of the boss at one point along the circumference and extending the length of the boss. When the receptacle is subsequently force fit into the bore of the boss, radially expansive forces are exerted on the walls of the boss tending to rupture the boss at the weld line. Where the part does not rupture during manufacture, strain is set up in the expanded plastic material that tends to rupture the part at a later time. When the material is unduly weak, the bosses have a tendency to crack prematurely in the field, after the telephone set has been installed on a customer's premise.